1. Technical Field
The embodiments herein generally relate to wireless communication, and, more particularly, to a highly reliable, fault tolerant, ad-hoc wireless mesh network and related methods of operation.
2. Description of the Related Art
Contemporary wireless communication networks (“networks”) typically allow simultaneous communication between several independently operating wireless devices. In order to provide the simultaneous communication, it is important that the devices do not interfere with each other's transmissions and to ensure that devices sending and receiving messages are properly tuned and synchronized with respect to each other. Devices capable of interfering with each other's transmissions are referred to as adjacent devices.
In order for transmissions to be properly sent and received, it is important that no two adjacent devices transmit data over the same communication channel at the same time, an event referred to as a collision. Where two adjacent devices transmit data over the same communication channel at the same time, it typically results in interference, making it difficult for intended recipients of the transmissions to disentangle originally transmitted data.
A common approach used in radio frequency (RF) communication in an effort to ensure that no two adjacent devices transmit over the same communication channel at the same time is to divide the available RF spectrum into fixed quanta called “frequency channels”, divide time into fixed quanta called “timeslots” which are aggregated into fixed groups called “frames”, and allow transmitters to send data using different frequency channels or different timeslots. An example of this type of communication is frequency hopping spread spectrum communication.
In a wireless network where both the RF spectrum and time are divided up, each separate combination of a particular “frequency channel” and a particular “timeslot” constitutes a unique “communication mode” that does not interfere with other communication modes in the network. Where the available RF spectrum is divided into many frequency channels and time is divided into many timeslots, each device in the network has a large number of non-interfering communication modes that it can use to communicate, thus making it possible for a large number of devices to participate in the network without interference. In addition, since the transmissions of two devices can only cause interference if the two devices are within RF range of one another, the likelihood of interference between devices can be further reduced by manipulating the spacing of the devices and the power level of the transmissions within a network.
FIG. 1 illustrates a wireless communication network including a plurality of wireless devices “A” through “R”. Devices that are within RF range of each other (referred to as “adjacent devices”) have a line drawn between them. For example, devices “A”, “B”, and “C” are within RF range of each other. Hence, in order to ensure that transmissions involving devices “A”, “B”, or “C” are properly sent and received, no two of these devices may transmit on the same frequency channel during the same timeslot. In addition, in order for device “A” to successfully transmit data to devices “B” and “C” using a particular frequency channel and a particular timeslot, devices “B” and “C” must tune their receivers to the particular frequency channel during the particular timeslot in order to receive the message.
FIG. 2 illustrates an exemplary set of communication modes for a wireless network configuration. In FIG. 2, time is divided into sequential frames comprising 24 timeslots each, and the available RF spectrum is divided into 50 frequency channels. The beginning of a frame (timeslot 1) will be referred to as a “frame time” or a “synchronized time reference”. Each box in the grid shown in FIG. 2 represents one communication mode. For a particular frame of time, the number of available communication modes is the number of timeslots multiplied by the number of frequency channels, or in this case, 50*24=1200 modes.
Although dividing time and available RF bandwidth helps limit the amount of interference in a wireless network, it creates a complication for the devices of figuring out which frequency channels and timeslots the other devices are using. In order for a communication to succeed, a device transmitting data and a device receiving the transmitted data must both use the same timeslot and frequency channel. Since wireless networks often involve a large number of frequency channels and timeslots, the likelihood that a particular pair of devices will use the same frequency channel/timeslot combination by chance alone is very slim. As a result, it is necessary for devices to coordinate their communications in some structured way. For example: networks that use timeslot assignment require mechanisms to synchronize the timing of adjacent transmitters and receivers to ensure successful communication.